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Re: Help with using wallclock
- From: Bart Veer <bartv at ecoscentric dot com>
- To: droethig at cipher dot com
- Cc: ecos-discuss at sources dot redhat dot com
- Date: Tue, 22 Feb 2005 19:06:41 +0000 (GMT)
- Subject: Re: [ECOS] Help with using wallclock
- References: <421B5DCF.4090201@cipher.com>
>>>>> "Dave" == David Roethig <droethig@cipher.com> writes:
Dave> I have some basic questions about the use of the wallclock package.
Dave> Currently, the following are defined:
Dave> CYGPKG_IO_WALLCLOCK
Dave> CYGSEM_WALLCLOCK_MODE : init_get
Dave> CYGPKG_WALLCLOCK_EMULATE
Dave> My basic misunderstanding is the relationship between the
Dave> application's view of time (HH:MM:SS DD MM YYYY) and how
Dave> this is updated/made current by the wallclock package.
Dave> I've read the documentation but I don't understand which the
Dave> application-level API calls can/should be used.
Dave> Are there functions/macros to convert from human-time to
Dave> seconds? (i.e. 14 Feb 2005 10:23:00 to xxx seconds since
Dave> 1970-01-01 00:00:00)
Dave> What is the relationship between libc time() and the
Dave> wallclock package?
The libc functions use the wallclock device to provide the current
time. Hence the API to access the wallclock consists of the standard C
library functions time(), strftime(), etc. A separate application
level API provided by wallclock devices would just lead to duplication
of code.
There is one extension to the standard C library,
cyg_libc_time_settime(), to update the wallclock device.
Dave> How is the emulated wallclock updated?
The eCos kernel has a system clock which normally ticks at 100Hz, and
the emulation wallclock device uses this to calculate a seconds value.
The base time is likely to be 00:00:00 UTC, January 1, 1970. Accuracy
depends on the underlying system clock.
Dave> My eventual goal is to use the RTC on the microcontroller we
Dave> are using (Sharp LH79520). This would change the
Dave> implementation but will it have an effect on the application
Dave> level interface?
Nope, the API stays the same but should give more useful results -
assuming the RTC is properly initialized.
Bart
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Bart Veer eCos Configuration Architect
http://www.ecoscentric.com/ The eCos and RedBoot experts
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